What is the Role of Genetics and Evolution in the Field of Psychology?

Genetics in Psychology: Studying how Genes affect Behavior

There are 23 pairs of chromosomes in our body; half of each pair comes from one parent, and the other half from another. Chromosomes are actually bundles of deoxyribonucleic acid or DNA. Segments of chromosomes that carry the hereditary code are called genes. We have approximately 60,000 genes in the body, half of which comes from the mother, and the other half from the father. Some traits, like eye color, are carried by a single gene, while most traits, especially the behavioral ones, are too complex to be determined by one gene alone. This is because certain traits require multiple genes in order to manifest, a phenomenon called Polygenic Inheritance. Additionally, genes follow the Dominant-Recessive Principle. This means that genes manifest only when they are dominant or when the genes acquired are both recessive. For example, I got my father's hazel brown eyes because it is dominant over my mother's black-colored eyes. However, if I instead got my father's recessive gene for black eyes and also my mother's, my eyes would have been black also like most Asians are.

Genetics started with Gregor Mendel, an Austrian monk who studied heredity by investigating generations of pea plants. He found that selective breeding leads a generation of pea plants to manifest one trait over another. Through this and other follow-up studies, Gregor Mendel was able to lay the foundations of genetics. Today, research findings in this field are increasingly being referred to by psychologists in their quest to study about behaviors and mental processes. Three of the methods that are being used today among geneticists are also being applied to the study of Psychology. They are molecular genetics, selective breeding and behavior genetics.

In Molecular Genetics, geneticists manipulate genes to determine its effects on behavior. At the heart of the Human Genome Project is to detect and correct genetic abnormalities, and to prevent one's susceptibility to certain kinds of diseases. This is where research on molecular genetics is oftentimes applied.

Using Selective Breeding, traits are reproduced by strengthening or weakening one gene over another. Recall the dominant-recessive principle discussed above. Examples of research employing selective breeding technique are Robert Tryon's (1940) 21 generations of maze-bright and maze-dull rats, and Dr. Robert Graham's Repository for Germinal Choice, the sperm bank of Nobel Prize Winners, located in Escondido, California.

In Behavior Genetics, geneticists assess how heredity influences the conduct of behavior. Twin Studies compare the behavioral attributes of identical and fraternal twins. (Note: Identical twins have the same sets of genes and shared their mother's womb during the prenatal stage, while fraternal twins have different sets of genes and they also shared their mother's womb during the prenatal stage.) Rose et al (1988) compared 7000 Finnish twins on extraversion and neuroticism, and found that identical twins are more similar than fraternal twins. The Minnesota Study of Twins Reared Apart by Thomas Bouchard (1996), based in Minneapolis, questioned and compared twins based on their family background, childhood environment, personal interests, vocational orientation, values, medical histories, lifestyle and habits. Interestingly, identical twins Jim Springer and Jim Lewis, who were separated at 4 weeks of age for 39 years, shared marked similarities. Both worked once as part-time deputy sheriffs, went to Florida for a vacation, owned Chevrolets, had a dog named Toy, married and divorced a woman named Betty, likes math, hates spelling, good at mechanical drawing, gained 10 pounds at about the same time in their lives, and suffered headache when they were 18 years old. On the other hand, Adoption Studies compare an adopted child with his biological and adopted parents, and his similarity with his biological and adopted siblings. For example, Scan and Weinberg (1983) found that a better predictor of adopted children's IQ scores is the educational level of their biological parents.

Research findings in genetics may lead the uncanny reader into thinking that "everything is in the genes." However, like most research studies, genetic research is filled with limitations and criticisms. Cooper and Zubeck (1958) found that maze-dull rats are significantly different from maze-bright rats only when both were reared in impoverished environments. Critics of twin studies claim that the social tendency to perceive and treat twins as set lead them into thinking and acting the same way, that similar homes (or environment) are decided by adoption agencies, that even strangers have coincidental similarities, and that most Minnesota twins were reunited several months before the study even began.

Evolution and Psychology: Behavior observed today can be traced way back yesterday.

The concept of evolution influences psychological research by expounding on the origin and development of behavior. Using evolution as an approach to study Psychology has lead to numerous studies about fear development (on strangers, snakes, spiders, heights, open spaces and darkness), perceptual adaptation (like tracking motion), children's imitation of higher-status people, and the worldwide preferences for kind, intelligent and dependable mates. It is said that these behaviors increased our chances of survival during the ancient days and that they continue to do so until now.

Criticisms on the Evolutionary Psychology Approach abounds. Albert Bandura, for one, rejected a one-sided evolution. He believes that evolution is not only shaped by nature, but that nature is also reconstructed by us humans, making us an important factor for leading the evolution of future generations. Steven Jay Gould (1981) commented that biological potentialities are mere instruments and not capable of dictating behavior. Lastly, Theodore Dobzhansky (1977) claimed that evolution is only artificial, that the adaptability of any living thing, especially us humans mean that behaviors are not fixed by what nature supposedly set upon us.